Challenges in Mechanics of Time-Dependent Materials, Mechanics of Biological Systems and Materials, and Micro-and Nanomechanics, Volume 2 of the Proceedings of the 2021 SEM Annual Conference & Exposition on Experimental and Applied Mechanics, the second volume of four from the Conference, brings together contributions to this important area of research and engineering. The collection presents early findings and case studies on fundamental and applied aspects of Experimental Mechanics, including papers in the following general technical research areas: Characterization Across Length ScalesExtreme Conditions & Environmental EffectsDamage, Fatigue and FractureStructure, Function and PerformanceRate Effects in ElastomersViscoelasticity & ViscoplasticityResearch in ProgressExtreme NanomechanicsIn-Situ NanomechanicsExpanding Boundaries in MetrologyMicro and Nanoscale DeformationMEMS for Actuation, Sensing and Characterization1D & 2D MaterialsCardiac MechanicsCell Mechanics Biofilms and Microbe MechanicsTraumatic Brain InjuryOrthopedic BiomechanicsLigaments and Soft Materials